Topological Defects in an Open Universe 1. Origin of Density Fluctua- Tions

This talk will explore the evolution of topological defects in an open universe. The rapid expansion of the universe in an open model slows defects and suppresses the generation of CBR fluctuations at large angular scale as does the altered relationship between angle and length in an open universe. Defect models, when normalized to COBE in an open universe, predict a galaxy power spectrum consistent with the galaxy power spectrum inferred from the galaxy surveys and do not require an extreme bias. Neither defect models in a flat universe nor standard inflationary models can fit either the multipole spectrum or the power spectrum inferred from galaxy surveys. The big bang theory, despite its successes in explaining the Hubble expansion, the thermal cosmic background radiation (CBR) and light element nucleosynthesis, is incomplete. For the big bang theory, the notion that the geometry and evolution of the universe is described by the Friedman-Robertson-Walker (FRW) metric, does not explain the origin of the density fluctuations that grew to form today's galaxies and large scale structure. There are two classes of extensions of the standard big bang model: either the universe began the FRW phase with density variations on scales that were then superhorizon or the universe began the FRW phase without fluctuations and subsequent causal physics generated density fluctuations. Models with primordial potential fluctuations can be classified as " curvature models " as they begin the FRW phase with variations in the space curvature. The generation of fluctuations in an initially smooth or " isocurvature " universe requires variations in the equation of state. Inflationary theories fall into the former category as they produce curvature fluctuations during a de-Sitter phase that predated the FRW phase. Models with topological defects fall into the latter category as strings or textures generate density fluctuations in initially smooth universes. There are a variety of physical mechanism that can lead to spatial variations in the equation of state. Peebles proposed that there are spatial variations in the ratio of baryons to photons. Since baryons and photons have different equations of state, these entropy fluctuations produce density fluctuations [1]. If there was a large-scale magnetic field, then its dynamics would lead to large-scale variations in the equation of state which would be another process that could produce density fluctuations. This talk explores topological defects, yet another mechanism that generates density fluctuations in an initial smooth universe through equation of …